When fluororubbers are vulcanized, hydrogen fluoride (HF) is generated by a vulcanizing reaction. Thus, fluororubber coating compositions contain acid acceptors to capture the generated hydrogen fluoride.
In general, oxides or hydroxides of calcium, magnesium, zinc, lead, etc. are used as acid acceptors contained in aqueous coating compositions of fluororubbers (see, for example, JP-A-56-47455 and JP-A-02-248453). However, these inorganic compounds have low dispersion stability in aqueous compositions. Therefore, even when they are dispersed to primary particles, they quickly form secondary agglomerates and form agglomerated materials in the coated films, or such agglomerates deteriorate the storage stability of the aqueous coating compositions of fluororubbers themselves (only main parts containing acid acceptors in the case of two-pack type ones).